The 'Heroes' actress - who celebrated her 20th birthday yesterday (21.08.09) - has been seen walking hand-in-hand with 28-year-old millionaire Harry Morton on a Miami beach, sparking rumours they are an item.

It is believed 'Mean Girls' actress Lindsay - who is dating on/off girlfriend, DJ Samantha Ronson - will be annoyed with the romantic developments.

A source said: "Lindsay won't be happy Hayden is dating her ex. Although she's with Sam Ronson, she is still pals with Harry."

The couple were laughing and frolicking on the seafront as they took the nightclub owner's two dogs for a walk.

It is also thought Hayden's ex-boyfriend, British TV presenter Steve Jones, will be "gutted" about Hayden's new man.

A source told Britain's Daily Mirror newspaper: "Steve will be totally gutted by this. He may be one of the hottest bachelors around but Hayden is one hell of a catch. And Harry is quite a contender too. He's so charming and it doesn't hurt that he is absolutely minted."

Harry and Lindsay dated in 2006, shortly before she met Samantha.

The restaurant owner broke up with the 23-year-old actress just weeks after they attended the Venice Film Festival together.

Hayden and Steve were seen cosying up at the Cannes Film Festival earlier this year.